A flexible fuel vehicle (FFV) is a vehicle that is operable with a fuel mixture comprising a basic fuel and an alternative fuel. The basic fuel is for example petrol and the alternative fuel is for example ethanol. At appropriate filling stations for example a petrol-ethanol mixture is sold, the ethanol component of which lies between 0% and 85%. Depending on the alternative fuel component, a different fresh air mass is required for full combustion of a defined fuel mixture quantity.
From U.S. Pat. No. 5,182,942 A, a method of determining an ethanol component in a fuel mixture is known. For this purpose a sample of the fuel mixture is heated and its evaporation temperature is acquired. In dependence upon the evaporation temperature the ethanol content of the fuel is inferred.